ww2 ammo tubes?

Yes, one round per tube. The tubes were cardboard coated with tar. A crate would hold several tubes and when they got to the vehicle the crate was busted open and the ammo was stowed in the vehicle, sometimes still in the tube.

The rounds are stored in black tar paper tubes, called tootsie rolls because they resemble the candy. The tubes are stored in a wooden crate, normally two rounds per crate. The tootsie rolls protect the rounds from josting and moisture damage.

where should i put them? would they be found on the back of a tank?

Possibly on the back of a tank or in a diorama setting where the tank is getting resupplied.

I don't think they would be in the vehicle, but anything is possible (including death rays from mars). I agree with Rob, re supply diorama or something like that, you could have tootsie rolls laying about. The turret is a tight place. getting the rounds out inside the turret would be very slow(deadly). We used to fill up the racks and then stack em in the floor. The naked rounds went downrange first.

what about a tank on the battle field. as if they were there for incase they run low after a battle and might not be getting resupplied for a while.